The present invention relates to a phase/digital conversion method as defined in the preamble of claim 1 and to arrangements for implementing the method.
Such methods and arrangements are of importance for the use of digital signal processing and its known advantages with very high frequency signals. In the past, the so-called "digitalization" of high and very high frequencies (f&gt;0.5 GHz) could not be solved in a technically satisfactory manner. However, the demand for such "signal quantizers" (A/D converters) for real time signal processing in satellite radio, satellite television, space travel radio, directional radio, radar and for digital ultrahigh frequency receivers has increased considerably in all commercial and military applications. At present, this trend is decisively supported by the likewise increasing appearance of novel, monolithically integrated microwave circuits (MMIC's) and digital circuits (in gigabit logic) in FaAs-FET and high speed ECL (emitter coupled logic) technology.
In the available fast A/D converters, there appears a separation with respect to resolution (word length) and speed (sampling rate). At present, the limits of the sampling and conversion rates for a word length of L.ltoreq.8 bits lie in a range from 100 MHz to 200 MHz and, for this reason alone, are not applicable for signals in the GHz range (microwave range).
Moreover, these fast A/D converters have a basic drawback resulting from amplitude quantization and their conversion rate is decisively limited by the frequency multiplication effect in the individual active A/D converter components. This effect results from the signal quantization of partially periodical, sawtooth-shaped or ramp-shaped transmission characteristics for binary coded A/D converters and convolution A/D converters. Due to the 2.sup.L periods (intervals) of these quantization characteristics, the bandwidth B.sub.s of a bandwidth limited input signal s(t) is increased within the A/D converters to a maximum bandwidth of EQU B.sub.U .ltoreq.2.sup.L .multidot.B.sub.s ( 1)
where L =the A/D converter word length in bits if the A/D converters are driven over their full range.
Today, Si-bipolar transistors reach transit frequencies of about 10 GHz. In a roughly calculated example according to Equation (1) for a prior art A/D converter having a word length of L =8 bits and such transistors, a bandwidth B.sub.s .ltoreq.50 MHz results for an input signal s(t) that can still be converted without errors by the A/D converter.
In contrast thereto, the sampling rate of such an A/D converter can be significantly higher than 2.multidot.B.sub.s =100 MHz. However, this does not improve the internal "quantization accuracy" and bandwidth of the A/D converters.
In order to substantially avoid these extreme bandwidth requirements to be met by the individual A/D converter components in the conventional methods for the digitalization of microwaves, principally different methods must be found.
Since the relevant information in most high frequency and microwave signals is contained only in their phase and frequency curves, the customary amplitude quantization can be replaced by a corresponding, equivalent phase quantization. Instead of analog/digital converters, phase/digital converters are then required.
Compared to amplitude digitalization, phase digitalization is possible up to significantly higher frequencies and signal bandwidths.
Reference /3/ describes and compares arrangements and methods for amplitude as well as phase digitalization. Phase/digital conversion is here based on a complex input signal whose in-phase (I) and quadrature (Q) components are fed into combination network. The output signals of the combination network are applied to the inputs of a plurality of comparators whose outputs are again connected with a coder for the generation of binary coded values for the momentary signal phase.